Gustave-Joseph Viseur, known as Gus Viseur, born on 15 May 1915 in Lessines (province of Hainaut, Belgium) and died on 25 August 1974 in Paris, was a Belgian accordionist.

Gus Viseur played all the genres of the musette repertoire (waltz, tango, paso doble...) and was one of the first jazz accordionists. Evolving in Parisian circles from 1930 onwards, he formed his musical language alongside Manouche guitarists, recorded his first album in 1937 and accompanied Édith Piaf in 1940. He is one of the only accordionists, along with Charles Verstraete, to have been a member of the famous Hot Club de France led by Charles Delaunay and Hugues Panassié.

He is the father-in-law of Joss Baselli, who married his daughter Josette Viseur.